本申请是申请日为2016年10月06日、申请号为201680058937.1、题为“用于利用持续换能器振动进行超声弹性成像的系统和方法”的分案申请。This application is a divisional application with application date of October 6, 2016, application number 201680058937.1, and titled “System and method for ultrasonic elastic imaging using continuous transducer vibration”.
相关-申请的交叉引用Related-Application Cross-Reference
本申请要求于2015年10月8日提交的标题为“SYSTEMS AND METHODS FORULTRASOUND ELASTOGRAPHY WITH CONTINUOUS TRANSDUCER VIBRATION(用于利用持续换能器振动进行超声弹性成像的系统方法)”的美国临时专利申请序列号62/238,891的权益。This application claims the benefit of U.S. Provisional Patent Application Serial No. 62/238,891, filed on October 8, 2015, entitled “SYSTEMS AND METHODS FOR ULTRASOUND ELASTOGRAPHY WITH CONTINUOUS TRANSDUCER VIBRATION”.
关于联邦政府赞助的研究的声明Statement Regarding Federally Sponsored Research
本发明是在美国国家卫生研究院授予的DK106957下利用政府支持完成的。美国政府享有本发明的某些权利。This invention was made with government support under DK106957 awarded by the National Institutes of Health. The U.S. Government has certain rights in this invention.
技术领域Technical Field
本发明的领域是用于超声弹性成像的系统和方法。更具体地，本发明涉及用于处理使用超声弹性成像获取的数据的系统和方法。The field of the invention is systems and methods for ultrasound elastography. More specifically, the invention relates to systems and methods for processing data acquired using ultrasound elastography.
背景技术Background Art
超声剪切波弹性成像(“SWE”)已经作为新的超声成像技术出现，所述技术可以非侵入性且量化地估定组织机械特性，所述组织机械特性是组织健康状态的较强生物标记。通常，在SWE中，将剪切波引入组织中，并且使用脉冲-回波超声检测剪切波的传播参数。然后，剪切波的检测用于计算与组织机械特性相关的参数，包括剪切波传播速度、扩散(即，频率相依性)、剪切波衰减、剪切模量、剪切粘度、杨氏模量、存储模量、损耗模量、损耗正切角和机械弛豫时间。Ultrasonic shear wave elastography ("SWE") has emerged as a new ultrasound imaging technique that can non-invasively and quantitatively assess tissue mechanical properties, which are strong biomarkers of tissue health. Typically, in SWE, shear waves are introduced into the tissue, and pulse-echo ultrasound is used to detect the propagation parameters of the shear waves. The detection of shear waves is then used to calculate parameters related to the mechanical properties of the tissue, including shear wave propagation velocity, diffusion (i.e., frequency dependence), shear wave attenuation, shear modulus, shear viscosity, Young's modulus, storage modulus, loss modulus, loss tangent, and mechanical relaxation time.
常规超声SWE使用声学辐射力(“ARF”)来在组织中生成剪切波。ARF需要从超声换能器传输长持续时间的推动脉冲，这要求在下一次传输之前很长的冷却时间，从而避免可能的探测和组织加热。这从根本上限制了超声SWE的帧速率(例如，限制为大约1Hz)。ARF还具有对超声系统的高电源要求，这使得在中端和低端超声扫描器中实现有挑战性。Conventional ultrasonic SWE uses acoustic radiation force ("ARF") to generate shear waves in tissue. ARF requires the transmission of long duration push pulses from the ultrasonic transducer, which requires a long cool-down period before the next transmission to avoid possible detection and tissue heating. This fundamentally limits the frame rate of ultrasonic SWE (e.g., to about 1 Hz). ARF also has high power requirements for the ultrasound system, which makes it challenging to implement in mid-end and low-end ultrasound scanners.
为了解决这些限制，利用超声换能器的持续振动的超声弹性成像技术(例如，在共同待决美国专利申请序列号62/072,167中所描述的技术)。这种技术通过换能器的持续振动来生成剪切波，并且利用相同的换能器来检测已生成的剪切波信号。因为这种技术不使用ARF来进行剪切波生成，所以这种技术允许持续的高帧速率剪切波成像以及利用中端和低端超声系统的便利实现方式。To address these limitations, ultrasound elastography techniques using continuous vibration of an ultrasound transducer (e.g., techniques described in co-pending U.S. patent application Ser. No. 62/072,167) are used. This technique generates shear waves by continuous vibration of the transducer and uses the same transducer to detect the generated shear wave signals. Because this technique does not use ARF for shear wave generation, this technique allows continuous high frame rate shear wave imaging and convenient implementation using mid-range and low-end ultrasound systems.
然而，换能器的持续振动还引入了剪切波信号处理的挑战。一个主要挑战是针对换能器的运动校正所获取数据，并且另一个主要挑战是利用逐行扫描超声系统成像时的运动信号对准。However, the continuous vibration of the transducer also introduces challenges in shear wave signal processing. One major challenge is correcting the acquired data for the motion of the transducer, and another major challenge is motion signal alignment when imaging with a progressive scanning ultrasound system.
发明内容Summary of the invention
本发明通过提供一种用于使用具有换能器的超声系统来测量对象的机械特性的方法克服了前述缺点。持续振动被提供至所述超声换能器，由此所述超声换能器的振动在所述对象中引入至少一个剪切波。然后，使用超声换能器从所述对象处获取所述运动数据。所述运动数据指示在所述对象内传播的所述至少一个剪切波。然后指示由所述超声换能器的持续振动造成的所述对象的变形的压缩简档被估计并且被用于通过将所述压缩简档从所述所获取运动数据中解调、分离或以其他方式去除来产生校正数据。然后对所述校正数据进行处理以计算所述对象的机械特性。The present invention overcomes the aforementioned disadvantages by providing a method for measuring the mechanical properties of an object using an ultrasonic system having a transducer. Continuous vibration is provided to the ultrasonic transducer, whereby the vibration of the ultrasonic transducer introduces at least one shear wave in the object. Then, the motion data is acquired from the object using the ultrasonic transducer. The motion data indicates the at least one shear wave propagating within the object. A compression profile indicating the deformation of the object caused by the continuous vibration of the ultrasonic transducer is then estimated and used to generate correction data by demodulating, separating or otherwise removing the compression profile from the acquired motion data. The correction data is then processed to calculate the mechanical properties of the object.
本发明的另一方面是提供一种用于使用具有换能器的超声系统来测量对象的机械特性的方法。持续且周期性振动被提供用于所述超声换能器，由此所述超声换能器的振动在所述对象中引入至少一个剪切波。然后，使用超声换能器从所述对象处获取所述运动数据。所述运动数据指示在所述对象内传播的所述至少一个剪切波，并且所述运动数据是在被选择用于减轻运动误差的时间点获取的，所述误差可归因于由所述持续且周期性振动造成的所述对象的变形。然后对所述运动数据进行处理以计算所述对象的机械特性。Another aspect of the present invention is to provide a method for measuring mechanical properties of an object using an ultrasonic system having a transducer. Continuous and periodic vibrations are provided for the ultrasonic transducer, whereby the vibrations of the ultrasonic transducer induce at least one shear wave in the object. Then, the motion data is acquired from the object using the ultrasonic transducer. The motion data indicates the at least one shear wave propagating within the object, and the motion data is acquired at a time point selected to mitigate motion errors attributable to deformations of the object caused by the continuous and periodic vibrations. The motion data is then processed to calculate the mechanical properties of the object.
本发明的另一方面是提供一种用于使用具有换能器的超声系统来测量对象的机械特性的方法。剪切波包括在对象中并且使用采用脉冲-回波模式的所述超声换能器从所述对象处获取运动数据。所述运动数据指示在所述对象内传播的所述剪切波。然后，由于所述对象中不同位置处的数据获取之间的时间延迟造成的误差而对所述运动数据进行校正，并且处理校正数据以计算所述对象的机械特性。Another aspect of the present invention is to provide a method for measuring mechanical properties of an object using an ultrasound system having a transducer. Shear waves are included in the object and motion data is acquired from the object using the ultrasound transducer in pulse-echo mode. The motion data is indicative of the shear waves propagating within the object. The motion data is then corrected for errors due to time delays between data acquisition at different locations in the object, and the corrected data is processed to calculate the mechanical properties of the object.
本发明的前述及其他方面和优点从以下说明书中将变得明显。在说明书中，参照在此构成其一部分的附图，并且在附图中通过图示的方式示出了本发明的优选实施例。然而，这样的实施例并不一定表示本发明的全部范围，并且因此参考权利要求书并在此用于解释本发明的范围。The foregoing and other aspects and advantages of the present invention will become apparent from the following description. In the description, reference is made to the accompanying drawings which form a part hereof and in which preferred embodiments of the present invention are shown by way of illustration. However, such embodiments do not necessarily represent the full scope of the present invention and therefore reference is made to the claims and are used herein to interpret the scope of the present invention.
附图说明BRIEF DESCRIPTION OF THE DRAWINGS
图1是示例超声系统的框图，所述超声系统实现了超声换能器的持续振动以将剪切波引入对象中。1 is a block diagram of an example ultrasound system that implements sustained vibration of an ultrasound transducer to introduce shear waves into a subject.
图2A至2C展示了使用超声换能器的持续振动在对象中引入剪切波和附加变形的示例。2A to 2C illustrate an example of using sustained vibration of an ultrasound transducer to induce shear waves and additional deformation in an object.
图3是流程图，阐述了用于响应于连续振动的超声换能器而获取运动数据并且针对换能器振动的效应来校正所获取数据的示例方法的步骤。3 is a flow chart setting forth the steps of an example method for acquiring motion data in response to a continuously vibrating ultrasound transducer and correcting the acquired data for the effects of transducer vibration.
图4A至4B展示了估计来自从所获取运动数据生成的k空间数据的压缩简档的示例。4A-4B illustrate examples of estimating a compression profile from k-space data generated from acquired motion data.
图5展示了实现在表示连续换能器振动的正弦信号的波峰(圆形)和波谷(方形)附近的脉冲-回波运动检测的示例。FIG. 5 shows an example of implementing pulse-echo motion detection around the peaks (circles) and troughs (squares) of a sinusoidal signal representing continuous transducer vibration.
图6展示了运动信号对准方法的示意曲线。运动检测的时间对准展示在区域1内。针对区域2描绘所提出的区域间对准方法。实心方形指示实际脉冲回波事件。空心圆形指示适时插入的数据点。具有虚线轮廓的灰色方形指示基于区域间对准的时移运动信号数据点。Fig. 6 shows a schematic graph of the motion signal alignment method. The temporal alignment of motion detection is shown in region 1. The proposed inter-region alignment method is depicted for region 2. The solid squares indicate actual pulse echo events. The hollow circles indicate the data points inserted in time. The grey squares with dashed outlines indicate the time-shifted motion signal data points based on the inter-region alignment.
图7展示了使用相移技术的剪切波信号对准的示例。Figure 7 shows an example of shear wave signal alignment using the phase shifting technique.
图8展示了用于低PRFe单一成像区域组织运动检测的混叠校正方法的示意曲线。上半部分示出了实际采样点与正弦波信号之间的关系。下半部分示出了恢复非混叠正弦信号的时移采样点。Figure 8 shows a schematic diagram of the aliasing correction method for low PRFe single imaging area tissue motion detection. The upper part shows the relationship between the actual sampling points and the sine wave signal. The lower part shows the time-shifted sampling points to restore the non-aliased sine signal.
图9描绘了传播剪切波和非传播压缩简档的k空间表示。FIG9 depicts a k-space representation of propagating shear waves and non-propagating compression profiles.
具体实施方式DETAILED DESCRIPTION
在此描述的是用于处理使用超声弹性成像获取的数据的系统和方法，在所述系统和方法中，使用超声换能器的持续振动在对象中生成剪切波。在此描述的系统和方法可以有效地去除与所述超声换能器的振动相关联的运动伪影，并且还可以去除逐行成像模式用于获取数据(如许多常规超声扫描器完成的那样)时所造成的数据采样未对准。Described herein are systems and methods for processing data acquired using ultrasound elastography, in which shear waves are generated in a subject using continuous vibration of an ultrasound transducer. The systems and methods described herein can effectively remove motion artifacts associated with the vibration of the ultrasound transducer, and can also remove data sampling misalignment caused when a line-by-line imaging mode is used to acquire data (as is done with many conventional ultrasound scanners).
因此，在此描述的系统和方法提供用于换能器运动校正以及用于对准由逐行扫描超声系统检测的运动信号的技术。Thus, the systems and methods described herein provide techniques for transducer motion correction and for aligning motion signals detected by a progressive scanning ultrasound system.
首先参照图1，展示了用于将剪切波引入对象20的示例系统10。在这一系统中，换能器12通过致动器14而机械振动，这使得换能器12在轴向方向(例如，图1中的z方向)上振荡。作为一个示例，致动器14可以是机械致动器，如，音圈致动器。当换能器12在轴向方向上移动时，剪切波16被引入到对象18之内。还可以从压缩波的模式变换中产生剪切波16。然后由在脉冲-回波模式中操作的相同超声换能器12检测所产生的剪切波16以提供对所述对象的机械特性的定量测量。Referring first to FIG. 1 , an example system 10 for introducing shear waves into an object 20 is shown. In this system, a transducer 12 is mechanically vibrated by an actuator 14, which causes the transducer 12 to oscillate in an axial direction (e.g., the z direction in FIG. 1 ). As an example, the actuator 14 can be a mechanical actuator, such as a voice coil actuator. As the transducer 12 moves in the axial direction, shear waves 16 are introduced into the object 18. The shear waves 16 can also be generated from a mode transformation of a compression wave. The generated shear waves 16 are then detected by the same ultrasonic transducer 12 operating in a pulse-echo mode to provide a quantitative measurement of the mechanical properties of the object.
致动器14耦合到超声换能器12。作为一个示例，致动器14可以直接附接到换能器12的外表面。出于说明目的，致动器14附接到图1中的换能器12的一侧。然而，在一些申请中，可以优选地将致动器与换能器12同轴地对齐，从而使得换能器运动主要与最小横向和纵向运动同轴。这一设置消除了对于单独振动源的需要，并且因此允许进行方便的单手操作。所述振动优选地是持续的以允许测量的持续更新。The actuator 14 is coupled to the ultrasonic transducer 12. As an example, the actuator 14 can be attached directly to the outer surface of the transducer 12. For illustration purposes, the actuator 14 is attached to one side of the transducer 12 in FIG. 1 . However, in some applications, it may be preferable to align the actuator coaxially with the transducer 12 so that the transducer motion is primarily coaxial with minimal lateral and longitudinal motion. This arrangement eliminates the need for a separate vibration source and thus allows for convenient one-handed operation. The vibration is preferably continuous to allow for continuous updating of the measurement.
超声换能器12可以沿超声波轴向或者取决于所期望的成像申请在其他方向上轴向地进行振动。可以操作用于剪切波检测的超声系统以通过平行波形成来检测单个A线、多个A线，或者利用平面波成像和软件波形成来检测整个2D面积或3D体积，如在超声扫描仪中完成。The ultrasound transducer 12 may be vibrated axially along the ultrasound axis or in other directions depending on the desired imaging application. The ultrasound system for shear wave detection may be operated to detect a single A-line, multiple A-lines by parallel wave forming, or an entire 2D area or 3D volume using plane wave imaging and software wave forming, as in This is done in an ultrasound scanner.
通过致动器14施加至超声换能器12的持续振动可以包含多种频率，并且因此可以处理所检测的剪切波以解析所述对象的取决于频率的特性。例如，所述处理可以沿时间维度使用带通滤波器以便仅选择某一时间处的一种频率，并且如果收集具有单一振动频率的数据，则后续处理将与其相同。多频率振动可以加速采集以便进行分散分析。利用持续振动和持续剪切波检测和处理，可以采用基本上实时的方式来持续地更新弹性成像测量。The continuous vibration applied to the ultrasonic transducer 12 by the actuator 14 can contain multiple frequencies, and thus the detected shear waves can be processed to resolve frequency-dependent characteristics of the object. For example, the processing can use a bandpass filter along the time dimension to select only one frequency at a certain time, and the subsequent processing will be the same if data with a single vibration frequency is collected. Multi-frequency vibration can speed up acquisition for decentralized analysis. Using continuous vibration and continuous shear wave detection and processing, elastic imaging measurements can be continuously updated in a substantially real-time manner.
当换能器12在轴向方向上振动时，如当振动对于换能器12的有源表面20是正常的时，换能器12的运动将损害在对象18中所检测的剪切波信号。由于超声运动检测将换能器12用作非移动参考坐标，因此这一信号损害是存在的，但是当换能器12由于外部振动而震荡时，则违背了这个假设。因此，为了适当地测量来自所检测剪切波的机械特性，需要校正由致动器14造成的换能器12的运动。When the transducer 12 vibrates in the axial direction, such as when the vibration is normal for the active surface 20 of the transducer 12, the movement of the transducer 12 will impair the shear wave signal detected in the object 18. This signal impairment exists because ultrasonic motion detection uses the transducer 12 as a non-moving reference coordinate, but this assumption is violated when the transducer 12 oscillates due to external vibrations. Therefore, in order to properly measure the mechanical properties from the detected shear waves, it is necessary to correct for the movement of the transducer 12 caused by the actuator 14.
换能器运动校正Transducer motion correction
在本公开的一方面中，提供了用于在连续换能器振动期间校正换能器运动的系统和方法。在超声中，通过比较两个脉冲回波事件之间的超声回波信号的时移τ来进行组织运动的测量。因为在软组织中超声传播速度c是恒定的(通常假设c＝1540m/s),所以这种时移可以被转换至组织位移为：In one aspect of the present disclosure, a system and method for correcting transducer motion during continuous transducer vibration is provided. In ultrasound, the measurement of tissue motion is performed by comparing the time shift τ of the ultrasound echo signal between two pulse-echo events. Because the ultrasound propagation velocity c is constant in soft tissue (usually assumed to be c=1540 m/s), this time shift can be converted to tissue displacement as:
其中，因子二说明在脉冲回波超声检测中的往返距离。平均组织粒子速度v还可以通过以下进行计算：Wherein, factor two accounts for the round trip distance in pulse echo ultrasound testing. The average tissue particle velocity v can also be calculated as follows:
其中，δ是两个脉冲回波事件之间的时间间隔。有时，多个脉冲回波事件的复合用于形成单一回波集合，以便提高信噪比(“SNR”)。在这种情况下，复合的脉冲回波事件各自可以由多个发送-接收过程组成。如在此使用的，术语“运动”可以包括位移、速度、加速度等。Wherein, δ is the time interval between two pulse-echo events. Sometimes, a compound of multiple pulse-echo events is used to form a single echo set in order to improve the signal-to-noise ratio ("SNR"). In this case, the compounded pulse-echo events may each consist of multiple transmit-receive processes. As used herein, the term "motion" may include displacement, velocity, acceleration, etc.
如以下在图2A至2C中展示的，并且如上所描述的，超声中的运动检测使用超声换能器作为参考坐标。然而，当以持续换能器振动来振动换能器自身时，换能器在运动以便产生剪切波。这具有若干效应。首先，运动检测的参考坐标正在移动，这在给定时刻为所有成像的像素或体元添加了恒定运动偏移量。第二，换能器在物理上推动组织并且在组织中造成压缩变形。由于这种效应引起的组织运动随着每个成像的像素或体元甚至在相同时刻的位置而变化。第三，振动的换能器在组织中产生剪切波，所述剪切波是用于估计组织机械特性的信号。因此，重要的是去除由于前两种效应引起的运动，以便恢复由于用于准确计算组织机械特性的剪切波而引起的运动。As shown below in Figures 2A to 2C, and as described above, motion detection in ultrasound uses the ultrasonic transducer as a reference coordinate. However, when the transducer itself is vibrated with continuous transducer vibration, the transducer is in motion so as to generate shear waves. This has several effects. First, the reference coordinate for motion detection is moving, which adds a constant motion offset to all imaged pixels or voxels at a given moment. Second, the transducer physically pushes on the tissue and causes compressive deformation in the tissue. The tissue motion due to this effect varies with the position of each imaged pixel or voxel even at the same moment. Third, the vibrating transducer generates shear waves in the tissue, which are signals used to estimate the mechanical properties of the tissue. Therefore, it is important to remove the motion due to the first two effects in order to recover the motion due to the shear waves for accurate calculation of the mechanical properties of the tissue.
图2A示出了由超声换能器12在组织对象18的顶表面上施加的均匀压缩dz。由组织变形引起的位移取决于组织的位置和材料特性两者。举例来讲，图2B中的黑线50示出了在时间点t1通过持续振动换能器进行压缩之后沿深度(例如，z方向)的位移变化。所述位移是在未压缩对象顶部的静止参考点集处测量的。由换能器测量的组织压缩被示出为图2B中的实灰线52，因为换能器表面在此被用作为参考坐标。由换能器测量的总组织运动(包括由于压缩引起的变形、以及换能器振动所造成的剪切波)被展示为图2B中的虚线54。FIG. 2A shows a uniform compression dz applied by an ultrasonic transducer 12 on the top surface of an object 18 of tissue. The displacement caused by the deformation of the tissue depends on both the position and material properties of the tissue. For example, the black line 50 in FIG. 2B shows the displacement change along the depth (e.g., z direction) after compression by a continuous vibrating transducer at time pointt1 . The displacement is measured at a stationary reference point set at the top of the uncompressed object. The tissue compression measured by the transducer is shown as the solid gray line 52 in FIG. 2B because the transducer surface is used as a reference coordinate here. The total tissue motion measured by the transducer (including the deformation caused by the compression and the shear wave caused by the transducer vibration) is shown as the dotted line 54 in FIG. 2B.
在图2C处示出了在第二时间点t2处的变形和剪切波运动。在图2C中展示的此示例中，由于换能器压缩引起的变形52较小(即，存在较小的dz)并且剪切波已传播通过介质，由针对总运动信号54沿z方向的相移所指出。The deformation and shear wave motion at a second time pointt2 is shown at Figure 2C. In this example shown in Figure 2C, the deformation 52 due to transducer compression is small (i.e., there is a small dz) and the shear wave has propagated through the medium, indicated by the phase shift in the z direction for the total motion signal 54.
现在参照图3，流程图展示为阐述了用于在持续换能器振动期间校正换能器运动的示例方法的步骤。所述方法总体上包括使用正在振动以在对象中生成剪切波的换能器从对象处获取数据，而数据是从所述对象中获取的，如在步骤302中所指示的。所获取数据指示在对象中总的所观察运动。在获取数据之后，估计表示数据获取期间换能器振动的压缩或变形简档，在步骤304中所指示的。根据多个不同的过程可以估计压缩简档，这在下面进行更详细地描述。使用所估计的压缩简档，将换能器运动的效应从所获取数据中解调、分离或以其他方式去除，如在步骤306中所指示的。作为一个示例，通过从所获取数据中减去压缩简档来从数据中去除换能器运动。根据校正数据，可以估计对象的机械特性，如步骤308处所指示的。Referring now to FIG. 3 , a flow chart is shown illustrating the steps of an example method for correcting transducer motion during sustained transducer vibration. The method generally includes acquiring data from an object using a transducer that is vibrating to generate shear waves in the object, and the data is acquired from the object, as indicated in step 302. The acquired data indicates the total observed motion in the object. After acquiring the data, a compression or deformation profile representing the transducer vibration during data acquisition is estimated, as indicated in step 304. The compression profile can be estimated according to a number of different processes, which are described in more detail below. Using the estimated compression profile, the effects of the transducer motion are demodulated, separated, or otherwise removed from the acquired data, as indicated in step 306. As an example, the transducer motion is removed from the data by subtracting the compression profile from the acquired data. Based on the corrected data, the mechanical properties of the object can be estimated, as indicated at step 308.
使用曲线拟合估计压缩简档Estimating compression profiles using curve fitting
作为一种用于估计压缩简档的示例方法，可以实现曲线拟合过程。在此方法中，通过将总运动(如图2B中虚线所描绘的)拟合至已知函数可以对压缩简档进行估计。举例来讲，已知函数可以包括以下各项中的一项或多项：指数、多项式、幂律、样条、Flamant解或Boussinesq解。在一些实施例中，为了说明材料特性的局部变化，多个函数可以用于在不同深度对多个空间窗口的压缩简档进行估计。空间窗口可以是一维、二维或三维窗口。As an example method for estimating the compression profile, a curve fitting process can be implemented. In this method, the compression profile can be estimated by fitting the total motion (as depicted by the dotted line in Figure 2B) to a known function. For example, the known function can include one or more of the following: an exponential, a polynomial, a power law, a spline, a Flamant solution, or a Boussinesq solution. In some embodiments, in order to account for local changes in material properties, multiple functions can be used to estimate the compression profile of multiple spatial windows at different depths. The spatial window can be a one-dimensional, two-dimensional, or three-dimensional window.
为了改进对压缩简档的估计，在曲线拟合过程之前，所测量的总运动可以被去噪。举例来讲，可以使用滤波或正则化方法实现去噪。In order to improve the estimation of the compression profile, the measured total motion can be denoised before the curve fitting process. For example, denoising can be achieved using filtering or regularization methods.
在此描述的方法可以使用各种方法扩展到更高维度的图像。在一个示例中，之前描述的拟合方法可以扩展到多维对应物，从而允许针对一个或多个帧执行对压缩的轴向、横向和时间估计。术语“帧”可以指在给定时间处获得的二维(“2D”)超声回波数据集合，并且随着时间推移可以在相同的2D平面处获得多个帧。在另一个示例中，沿每个横向位置处重复的单一1D简档执行拟合，这允许从整个成像帧中去除换能器运动效应。在其他实现方式中，单一变形简档可以被应用于图像内的每个横向位置，以便进一步缩短计算时间。这种过程还可以在每个获取帧上重复(即，应用于不同时刻)，以便随着时间推移校正来自整个获取的换能器运动。The methods described herein can be extended to higher dimensional images using various methods. In one example, the fitting method described previously can be extended to a multi-dimensional counterpart, allowing axial, lateral and time estimates of compression to be performed for one or more frames. The term "frame" can refer to a two-dimensional ("2D") ultrasound echo data set obtained at a given time, and multiple frames can be obtained at the same 2D plane over time. In another example, a single 1D profile repeated along each lateral position is performed to fit, which allows the transducer motion effect to be removed from the entire imaging frame. In other implementations, a single deformation profile can be applied to each lateral position within the image to further shorten the calculation time. This process can also be repeated on each acquisition frame (i.e., applied to different moments) to correct the transducer motion from the entire acquisition over time.
在上述曲线拟合示例中，从单一横向位置和单一帧沿着压缩方向估计换能器运动。像任何获取技术一样，所有的测量将包含一些误差。如此，利用来自多个空间位置和多个帧的信息将减少随机误差并且提供对真正压缩简档的更好估计。这可以通过至少两种方式来完成。In the curve fitting example above, the transducer motion was estimated along the compression direction from a single lateral position and a single frame. Like any acquisition technique, all measurements will contain some error. Thus, utilizing information from multiple spatial positions and multiple frames will reduce random errors and provide a better estimate of the true compression profile. This can be done in at least two ways.
在一种方法中，使用平均数、加权平均数、中值或类似技术来组合在若干相邻横向位置处测量的多个总观察运动信号，以便获得用于曲线拟合和减法的噪声较少的总运动测量结果。In one approach, multiple total observed motion signals measured at several adjacent lateral positions are combined using an average, weighted average, median, or similar technique to obtain a less noisy total motion measurement for curve fitting and subtraction.
在另一种方法中，对来自每个帧的压缩简档进行估计，所估计的简档被组合成单一压缩简档，并且组合的简档从每个帧中减去以便去除压缩效应。尽管每个帧将在不同的时间点处获得，并且将组织压缩至不同的程度，但是作为第一阶近似值，可以假设的是压缩简档将是相互幅度按比例缩放的版本。In another approach, the compression profile from each frame is estimated, the estimated profiles are combined into a single compression profile, and the combined profile is subtracted from each frame to remove the compression effect. Although each frame will be acquired at a different point in time and will compress the tissue to a different degree, as a first order approximation, it can be assumed that the compression profiles will be scaled versions of each other in magnitude.
因此，可以对在每个横向位置处的不同帧的所有单独的压缩简档进行归一化，从而使得简档进将被组合(例如，使用取平均值)成单一压缩简档以用于随机噪声被抑制的每个横向位置。组合的压缩简档可以被缩放，并拟合至各个帧，并且然后被减去，以便获得在所述横向位置处的真正剪切波运动。对于所有横向位置可以重复相同的过程，以便获得跨2D区域的剪切波信号以用于进一步处理。需注意，这两种技术不互斥并且可以彼此结合使用。Therefore, all individual compression profiles for different frames at each lateral position can be normalized so that the profiles will be combined (e.g., using averaging) into a single compression profile for each lateral position where random noise is suppressed. The combined compression profile can be scaled and fit to the individual frames and then subtracted to obtain the true shear wave motion at the lateral position. The same process can be repeated for all lateral positions to obtain the shear wave signal across the 2D region for further processing. Note that these two techniques are not mutually exclusive and can be used in conjunction with each other.
使用参考数据估计压缩简档Estimating compression profiles using reference data
作为另一种用于估计压缩简档的示例方法，可以获取并实现参考压缩简档。在此方法中，准静态压缩应用于对象并且通过使用相同的超声换能器的脉冲回波检测来对参考压缩简档进行估计。可以利用手动压缩或者通过以远低于在剪切波成像中典型使用的频率(例如，1Hz)来振动换能器从而实现准静态压缩。As another example method for estimating a compression profile, a reference compression profile can be obtained and implemented. In this method, quasi-static compression is applied to the object and the reference compression profile is estimated by pulse-echo detection using the same ultrasound transducer. Quasi-static compression can be achieved using manual compression or by vibrating the transducer at a frequency much lower than that typically used in shear wave imaging (e.g., 1 Hz).
可以假设，由于剪切波的运动在此情况中是可以忽略不计的；因此，所测量的运动简档应该只是由换能器压缩引起的。作为第一阶近似值，在不同压缩级别dz的压缩简档应该是彼此的缩放版本。因此，在单一压缩级别处获得的一个参考压缩简档应该是充足的。替代性地，多个压缩简档可以在不同压缩级别处获得，并且可以使用如上关于用于曲线拟合的组合压缩简档所描述的那些类似过程被缩放且被组合以形成具有更高信噪比(“SNR”)的单一参考压缩简档。It can be assumed that the motion due to shear waves is negligible in this case; therefore, the measured motion profile should be caused only by transducer compression. As a first order approximation, the compression profiles at different compression levels dz should be scaled versions of each other. Therefore, one reference compression profile obtained at a single compression level should be sufficient. Alternatively, multiple compression profiles can be obtained at different compression levels and can be scaled and combined to form a single reference compression profile with a higher signal-to-noise ratio ("SNR") using similar processes as those described above for combined compression profiles for curve fitting.
参考压缩简档可以被缩放、被拟合成所测得的总组织运动，并且从总组织运动中减去，以便获得真正的剪切波运动。以上关于曲线拟合所描述的空间和时间求平均技术还可以用在参考压缩方法中，以便提高SNR。The reference compression profile can be scaled, fitted to the measured total tissue motion, and subtracted from the total tissue motion to obtain the true shear wave motion.The spatial and temporal averaging techniques described above with respect to curve fitting can also be used in the reference compression method to improve the SNR.
使用计算模型估计压缩简档Estimating compression profiles using computational models
作为另一种用于估计压缩简档的示例方法，可以实现压缩简档建模。在此方法中，压缩简档可以从有限元方法(“FEM”)模拟或分析解决方案中获取。一旦已知已建模的压缩简档，其就可以被缩放、拟合并且从所测得的总组织运动中减去，如以上所述。作为第一近似值，对象可以被假设为均匀的。针对均匀介质，来自平坦表面换能器的压缩简档不应该随着介质的剪切模量而变化。因此，典型的剪切模量(比如，1kPa)可以用于这种建模。针对包含均匀材料或组织的对象，来自均匀假设的压缩简档可用于获得对象的2D弹性图像的一阶解决方案。然后，这种图像可用于运行另一种FEM模拟，以便获得更准确的压缩简档以用于更好地重建对象的真正2D弹性图像。As another example method for estimating a compression profile, compression profile modeling can be implemented. In this method, the compression profile can be obtained from a finite element method ("FEM") simulation or analysis solution. Once the modeled compression profile is known, it can be scaled, fitted and subtracted from the measured total tissue motion, as described above. As a first approximation, the object can be assumed to be uniform. For uniform media, the compression profile from a flat surface transducer should not change with the shear modulus of the medium. Therefore, a typical shear modulus (e.g., 1 kPa) can be used for this modeling. For objects containing uniform materials or tissues, the compression profile from the uniform assumption can be used to obtain a first-order solution for a 2D elastic image of the object. Then, this image can be used to run another FEM simulation to obtain a more accurate compression profile for better reconstruction of the true 2D elastic image of the object.
使用自适应估计对压缩简档进行估计Estimating compression profiles using adaptive estimation
作为另一种用于估计压缩简档的示例方法，可以实现自适应估计方法。在此方法中，通过将空间平均值、加权平均值、中值或类似技术应用于沿深度轴(即，z轴)在一系列小空间窗口中所测得的总运动，可以对压缩简档进行估计。空间窗口可以是一维、二维或三维窗口。设想的是，剪切波将在深度方向上循环并且当应用求平均过程时将减小。因此，在求平均过程之后，设想压缩简档将保持。类似于以上所描述的曲线拟合方法，这些自适应方法可以结合来自多个空间位置和时间实例的信息，从而提高所估计压缩简档的准确度和精度。这可以通过应用具有专门内核(比如，高斯或拉普拉斯内核)的多维卷积技术，或其他多维滤波器(比如，中值或双边滤波器)来完成。As another example method for estimating a compression profile, an adaptive estimation method can be implemented. In this method, the compression profile can be estimated by applying a spatial average, a weighted average, a median, or a similar technique to the total motion measured in a series of small spatial windows along the depth axis (i.e., the z-axis). The spatial window can be a one-dimensional, two-dimensional, or three-dimensional window. It is envisioned that the shear waves will circulate in the depth direction and will decrease when the averaging process is applied. Therefore, after the averaging process, it is envisioned that the compression profile will remain. Similar to the curve fitting method described above, these adaptive methods can combine information from multiple spatial locations and time instances to improve the accuracy and precision of the estimated compression profile. This can be accomplished by applying multidimensional convolution techniques with specialized kernels (e.g., Gaussian or Laplace kernels), or other multidimensional filters (e.g., median or bilateral filters).
去除k空间中的压缩简档Removal of compression profile in k-space
在一些情况中，不必估计压缩，而是压缩可以直接与剪切波解耦。如果跨换能器的全运动路径获取多个帧，从而使得运动在多个时间点(例如，帧)在深度方向(例如，z方向)以及横向方向(例如，x方向)两者上被获取，则传播剪切波信号可以从压缩中分离。这可以通过利用传播波和非传播运动的k空间表示的差异来完成。In some cases, compression need not be estimated, but compression can be directly decoupled from shear waves. If multiple frames are acquired across the full motion path of the transducer, such that motion is acquired at multiple time points (e.g., frames) in both the depth direction (e.g., z-direction) and the lateral direction (e.g., x-direction), then the propagating shear wave signal can be separated from the compression. This can be accomplished by exploiting the difference in the k-space representations of propagating waves and non-propagating motion.
如图9所示，对于在深度方向(例如，z轴)上传播的波，k空间kz-f平面(其中，kz表示深度方向上的波数并且f表示时间频率)中的频谱表示将包含两个共轭对称波峰90、92。第一波峰90位于与信号的正波数和时间频率对应的点处，并且第二波峰92径向对称于所述第一波峰并且位于与负波数和负时间频率对应的点处。因此，传播信号的k空间表示将出现在kz-f平面的非相邻象限中，并且跨kz轴不共轭对称。考虑到作为第一阶近似值，压缩简档将被幅度缩放，但是与k空间中的压缩简档相关联的非传播频谱信息94将跨kz轴共轭对称。在图9中示出了针对传播波和非传播压缩的k空间表示。As shown in FIG9 , for a wave propagating in the depth direction (e.g., z-axis), the spectral representation in the k-spacekz -f plane (wherekz represents the wave number in the depth direction and f represents the temporal frequency) will contain two conjugate symmetric peaks 90, 92. The first peak 90 is located at a point corresponding to the positive wave number and temporal frequency of the signal, and the second peak 92 is radially symmetric to the first peak and is located at a point corresponding to the negative wave number and negative temporal frequency. Therefore, the k-space representation of the propagated signal will appear in non-adjacent quadrants of thekz -f plane and will not be conjugate symmetric across thekz axis. Considering that as a first order approximation, the compression profile will be amplitude scaled, but the non-propagating spectral information 94 associated with the compression profile in k-space will be conjugate symmetric across thekz axis. The k-space representation for propagating waves and non-propagating compression is shown in FIG9 .
因为压缩简档跨kz轴共轭对称，而传播波不共享此相同的特性，所以通过利用这个对称差异可以将剪切波与压缩解耦。一种用于完成这个的方法是将k空间中的每个点表示为k(fM,kzN)，其中，fM和kzN表示限定k空间中单个点的时间频率和波数对中的一个。k(fM,-kzN)的复共轭可以被添加至限定在k空间中所有的点k(fM,kzN)，并且然后通过对k空间数据应用傅立叶逆变换可以恢复剪切波运动。为了恢复波传播，最初不包含剪切波信号的象限可以被衰减或设定为零，然后应用傅立叶逆变换。尽管这种方法在此描述用于在1D空间和1D时间中的波传播，但本领域技术人员将理解的是，这种方法可以轻易地扩展到2D空间、3D空间等。Because the compression profile is conjugate symmetric across thekz axis, while propagating waves do not share this same property, shear waves can be decoupled from compression by exploiting this symmetry difference. One method for accomplishing this is to represent each point in k-space as k(fM ,kzN ), wherefM andkzN represent one of a time frequency and wavenumber pair that defines a single point in k-space. The complex conjugate of k(fM ,-kzN ) can be added to all points k(fM ,kzN ) defined in k-space, and the shear wave motion can then be recovered by applying an inverse Fourier transform to the k-space data. In order to recover wave propagation, quadrants that initially do not contain shear wave signals can be attenuated or set to zero, and then an inverse Fourier transform is applied. Although this approach is described herein for wave propagation in 1D space and 1D time, those skilled in the art will appreciate that this approach can be easily extended to 2D space, 3D space, and the like.
对来自k空间的压缩简档进行估计Estimation of compression profile from k-space
作为另一种用于估计压缩简档的示例方法，可以从k空间对压缩简档进行估计。在此方法中，在给定的帧中沿所观察信号u(z)的深度轴(例如，z轴)应用傅立叶变换，以便获得频域表示U(kz)。这种频域表示可以被称为k空间。对于k空间中具有坐标kz的给定像素，距k空间的原点的距离表示此像素的空间频率。As another example method for estimating the compression profile, the compression profile can be estimated from k-space. In this method, a Fourier transform is applied along the depth axis (e.g., z-axis) of the observed signal u(z) in a given frame to obtain a frequency domain representation U(kz ). This frequency domain representation may be referred to as k-space. For a given pixel with coordinates kz in k-space, the distance from the origin of k-space represents the spatial frequency of this pixel.
可以假设，压缩简档正在缓慢增加并且平滑。因此，k空间中的变形信号还将保持平滑。然而，剪切波的k空间分量将位于k空间中与图像空间中波长对应的不同点处。这导致了与这些剪切波分量的频率相关联的kz的一个或多个值的振幅增加。当压缩和剪切波信号的k空间组合频谱被一起评估时，频谱将随着由于剪切波运动信号引起的一个或多个振幅不连续而平滑地变化。通过使用平均数、加权平均数、中值或其他滤波方法来去除与剪切波信号对应的k空间分量，可以获得对与压缩简档对应的频率分量的估计。所估计的压缩简档可以通过执行傅立叶逆变换以将k空间信号转变回至图像空间来产生。上述的空间求平均或帧求平均方法可以用于提高压缩简档估计的SNR。替代性地，当使用2D/3D空间区域和/或通过使用多个帧以包括时间维度时这种方法可以扩展至更高的维度。It can be assumed that the compression profile is slowly increasing and smoothing. Therefore, the deformation signal in k-space will also remain smooth. However, the k-space components of the shear wave will be located at different points in k-space corresponding to the wavelengths in image space. This results in an increase in the amplitude of one or more values ofkz associated with the frequencies of these shear wave components. When the k-space combined spectrum of the compression and shear wave signals is evaluated together, the spectrum will change smoothly with one or more amplitude discontinuities caused by the shear wave motion signal. By using an average, weighted average, median or other filtering method to remove the k-space components corresponding to the shear wave signal, an estimate of the frequency components corresponding to the compression profile can be obtained. The estimated compression profile can be generated by performing an inverse Fourier transform to convert the k-space signal back to image space. The above-mentioned spatial averaging or frame averaging method can be used to improve the SNR of the compression profile estimate. Alternatively, this method can be extended to higher dimensions when using 2D/3D spatial regions and/or by using multiple frames to include the time dimension.
这种过程总体上在图4A中展示，其中，正弦剪切波信号已经被添加至使用弹性材料(黑色点)的FEM模拟所模拟的压缩简档。使用傅立叶变换来转变至k空间，所产生的频谱具有与50m-1(图4B，实线)剪切波对应的单一频率分量。利用10m-1滑动窗口(从10至200m-1应用的)应用滑动中值滤波器导致经滤波的频谱(图4B，点划线)。经滤波的频谱没有与剪切波信号对应的波峰，并且当转换回到图像空间时提供由于换能器运动而引起的对压缩简档的估计(图4A，实线)。This process is generally illustrated in FIG4A , where a sinusoidal shear wave signal has been added to a compression profile simulated using an FEM simulation of an elastic material (black dots). Using a Fourier transform to transform to k-space, the resulting spectrum has a single frequency component corresponding to a 50 m−1 ( FIG4B , solid line) shear wave. Applying a sliding median filter using a 10 m−1 sliding window (applied from 10 to 200 m−1 ) results in a filtered spectrum ( FIG4B , dot-dash line). The filtered spectrum has no peaks corresponding to the shear wave signal and provides an estimate of the compression profile due to transducer motion when converted back to image space ( FIG4A , solid line).
在正弦波的波峰或波谷处的超声检测Ultrasonic testing at the peak or trough of a sine wave
在一些实施例中，不对压缩简档进行估计，而是对数据获取进行更改以最小化换能器运动的效应。具体地，对于正弦振动的换能器，在正弦信号的波峰和波谷附近的时刻处进行的脉冲回波检测可以抑制由于换能器压缩引起的组织变形。In some embodiments, the compression profile is not estimated, but the data acquisition is modified to minimize the effect of transducer motion. Specifically, for a transducer vibrating sinusoidally, pulse-echo detection at times near the peaks and troughs of the sinusoidal signal can suppress tissue deformation due to transducer compression.
如图5所示，当在对称于正弦波波峰的时间t1和t2(即，从t1至正弦波波峰的时间等于从正弦波波峰至t2的时间)进行运动检测的两个脉冲回波事件时，在两个时间t1和t2，换能器都将处于相同的压缩位置dz。通过在这些时间处获得数据，没有检测到组织变形，因为脉冲回波仅检测时间t1与t2之间的相对运动。因此，使用这种获取仅检测到传播的剪切波。As shown in FIG5 , when two pulse-echo events for motion detection are performed at timest1 andt2 that are symmetrical to the sine wave peak (i.e., the time fromt1 to the sine wave peak is equal to the time from the sine wave peak tot2 ), the transducer will be in the same compression position dz at both timest1 andt2 . By acquiring data at these times, no tissue deformation is detected because the pulse-echo only detects relative motion between timest1 andt2 . Therefore, only propagating shear waves are detected using this acquisition.
类似地，在正弦波波谷处的检测(图5中的方形)还可以被实现为抑制由于换能器压缩引起的组织变形。这种方法对于脉冲回波事件之间的不同时间间隔有效，只要时间间隔被置于对称于正弦波的波峰或波谷。然而，因为所检测的运动是这两个脉冲回波事件之间的平均运动，所以时间间隔Δt＝t2-t1不应该太长，以便为剪切波检测提供充足的时间分辨率。需注意，正弦信号是周期性的；因此，在除了t2的一个或多个完整循环处(比如图5中的t3)的检测事件与在t2处的检测事件完全相同。这允许在脉冲回波时序中的更多灵活性。Similarly, detection at the trough of the sine wave (square in FIG5 ) can also be implemented to suppress tissue deformation due to transducer compression. This approach is valid for different time intervals between pulse-echo events, as long as the time interval is placed symmetrically about the peak or trough of the sine wave. However, because the detected motion is the average motion between the two pulse-echo events, the time interval Δt=t2 -t1 should not be too long in order to provide sufficient time resolution for shear wave detection. Note that the sinusoidal signal is periodic; therefore, the detection event at one or more complete cycles other than t2 (such as t3 in FIG5 ) is exactly the same as the detection event at t2. This allows more flexibility in the pulse-echo timing.
在当换能器处于相同位置时不发生检测的情况下，随着换能器运动效应被最小化可以获得图像。这可以通过当检测关于运动简档的波峰和波谷对称时利用其他检测来恢复或估计运动来完成。这可以通过使用插值法、参数拟合或相移方法来执行。In the case where no detection occurs when the transducer is in the same position, an image can be obtained with the transducer motion effects minimized. This can be done by using other detections to recover or estimate the motion when the detections are symmetrical about the peaks and troughs of the motion profile. This can be performed using interpolation, parameter fitting, or phase shifting methods.
使用运动传感器来检测换能器运动Use motion sensors to detect transducer movement
作为另一种用于估计压缩简档的示例方法，可以通过利用耦合至或集成于超声换能器的运动传感器所获取的数据来估计压缩简档。在此方法中，用于测量加速度、速度、位移等的运动传感器可以耦合至超声换能器或集成在超声换能器内以测量其振动。这种方法提供了某些附加优势。作为一个示例，换能器的振动响应可能具有相较于用于驱动振动换能器的致动器的正弦信号的相位延迟。在这些实例中，测量换能器运动的传感器可以提供准确的同步以用于在如上述的正弦波的波峰或波谷处的超声检测。作为另一个示例，由运动传感器测量的换能器运动可用于在上述的运动减法方法中适当地缩放变形简档。因此，设想的是，使用运动传感器来测量换能器的运动可单独地或结合上述方法使用。As another example method for estimating a compression profile, a compression profile can be estimated by using data obtained by a motion sensor coupled to or integrated in an ultrasonic transducer. In this method, a motion sensor for measuring acceleration, velocity, displacement, etc. can be coupled to an ultrasonic transducer or integrated in an ultrasonic transducer to measure its vibration. This method provides certain additional advantages. As an example, the vibration response of the transducer may have a phase delay compared to the sinusoidal signal of the actuator used to drive the vibration transducer. In these instances, the sensor measuring the motion of the transducer can provide accurate synchronization for ultrasonic detection at the peaks or troughs of the sine wave as described above. As another example, the transducer motion measured by the motion sensor can be used to appropriately scale the deformation profile in the motion subtraction method described above. Therefore, it is envisioned that the use of a motion sensor to measure the motion of the transducer can be used alone or in combination with the above method.
作为使用运动传感器的替代方案，由移动的换能器检测到的静止目标的运动还可用于估计换能器的位置，并且用于提高用于在如上述的正弦波的波峰或波谷处的超声检测的同步的准确度。举例来讲，静止目标可以是在换能器视场中在较深位置(在所述位置中，剪切波被完全衰减)处的非移动骨架或组织目标。As an alternative to using a motion sensor, the motion of a stationary target detected by a moving transducer can also be used to estimate the position of the transducer and to improve the accuracy of synchronization for ultrasound detection at the peaks or troughs of a sine wave as described above. For example, the stationary target can be a non-moving skeletal or tissue target at a deeper position in the field of view of the transducer where the shear waves are completely attenuated.
对超声运动检测中时间延迟进行校正Correcting for time delay in ultrasonic motion detection
在本公开的一方面中，提供了用于对超声运动检测中时间延迟进行校正的系统和方法。在剪切波在组织中生成之后，可以使用脉冲回波运动检测来检测剪切波，如上所述。为了产生组织的机械特性的2D图像，期望对跨具有高时间分辨率的较大2D区域的组织运动进行同步检测。这可以通过“平面波”成像器来实现，在所述成像器中，来自2D检测区域内的每个像素的回波可以由平面超声波的单一传输进行重构。In one aspect of the present disclosure, systems and methods are provided for correcting for time delays in ultrasonic motion detection. After the shear waves are generated in the tissue, pulse-echo motion detection can be used to detect the shear waves, as described above. In order to produce a 2D image of the mechanical properties of the tissue, it is desirable to synchronize the detection of tissue motion across a larger 2D area with high temporal resolution. This can be achieved with a "plane wave" imager, in which the echo from each pixel within the 2D detection area can be reconstructed from a single transmission of planar ultrasound.
然而，大多数商业超声扫描器不使用平面波成像，而是仍然使用顺序逐行扫描方法，其中，多个脉冲回波事件需要覆盖2D检测区域。因此，逐行扫描器具有比平面波成像器显著更低的成像帧速率。此外，利用逐行扫描器，需要考虑2D成像区域内每个成像行之间的时间延迟，以便根据所检测的剪切波正确地计算组织的机械特性。下面描述用于解决利用逐行扫描器检测剪切波的这种挑战的若干技术。However, most commercial ultrasound scanners do not use plane wave imaging, but still use a sequential line-by-line scanning method, in which multiple pulse-echo events are required to cover the 2D detection area. Therefore, a line-by-line scanner has a significantly lower imaging frame rate than a plane wave imager. In addition, with a line-by-line scanner, the time delay between each imaging line within the 2D imaging area needs to be considered in order to correctly calculate the mechanical properties of the tissue from the detected shear waves. Several techniques for addressing this challenge of detecting shear waves using a line-by-line scanner are described below.
如图6所示，在逐行扫描器中实现的换能器12可以遵循某个顺序V1→V2→V3→...VN→V1→V2→...VN操作以按顺序且周期性地向换能器12的第一区域(例如，区域1)发出检测光束。As shown in FIG. 6 , the transducer 12 implemented in a progressive scanner may operate following a certain sequence V1 →V2 →V3 → ... VN →V1 →V2 → ... VN to sequentially and periodically emit a detection beam to a first region (eg, region 1 ) of the transducer 12 .
其中，V是成像矢量，每一个成像矢量包含在一个脉冲回波事件期间可以被平行地波束成形的n成像A行；N是每个成像区域内成像矢量的总数；并且M是在每个成像矢量位置处获取的脉冲回波事件的数量。图6中的实黑色方形表示脉冲回波事件的时刻，并且每个黑色方形附近的数字指示每个脉冲回波事件的时间序列。Wherein, V is an imaging vector, each imaging vector containing n imaging A rows that can be beamformed in parallel during one pulse-echo event; N is the total number of imaging vectors in each imaging region; and M is the number of pulse-echo events acquired at each imaging vector position. The solid black squares in FIG6 represent the moments of pulse-echo events, and the numbers near each black square indicate the time sequence of each pulse-echo event.
假设脉冲回波事件的脉冲重复频率是PRF0，然后，PRF0的上限受成像深度控制。每个矢量的有效脉冲重复频率是Assume that the pulse repetition frequency of the pulse-echo events is PRF0 , then the upper limit of PRF0 is controlled by the imaging depth. The effective pulse repetition frequency for each vector is
经常期望保持较高的PRFe，例如1kHz；因此，N应该足够小以维持较高的PRFe。然而，减少成像矢量的数量将减小每个区域的大小；因此，由于较小的N值，可能需要多个区域来覆盖较大的2D检测区域。It is often desirable to maintain a high PRFe , such as 1 kHz; therefore, N should be small enough to maintain a high PRFe . However, reducing the number of imaging vectors will reduce the size of each region; therefore, due to the smaller N value, multiple regions may be required to cover a larger 2D detection area.
如图6所示，在已经针对前一个区域(例如，区域1)中的每个矢量收集了所有M样本之后，顺序跟踪进行至换能器12的另一个区域(例如，区域2)。重复相同的跟踪顺序，直到已经针对区域2中的每个矢量收集了所有M样本。针对区域2的检测事件还由区域2下的黑色实方形表示。可以重复这个过程，直到所有区域中的数据都被收集。6 , after all M samples have been collected for each vector in the previous region (e.g., region 1), sequential tracking proceeds to another region (e.g., region 2) of the transducer 12. The same tracking sequence is repeated until all M samples have been collected for each vector in region 2. Detection events for region 2 are also represented by black solid squares under region 2. This process can be repeated until data in all regions is collected.
使用如图6所示的顺序跟踪方法所检测的运动信号存在两个问题。首先，在每个区域内检测事件时间上没有对准。第二，存在时间延迟，There are two problems with the motion signal detected using the sequential tracking method shown in Figure 6. First, the detection events in each area are not aligned in time. Second, there is a time delay.
在时间上相邻的区域之间(例如，区域1和区域2)。如以上所解释的，对组织机械特性的适当计算要求跨整个2D成像区域的运动信号应该具有相同的时间网格(即，应该是时间对准的)。Between temporally adjacent regions (eg, region 1 and region 2). As explained above, proper calculation of tissue mechanical properties requires that the motion signal across the entire 2D imaging region should have the same temporal grid (ie, should be time aligned).
用于在每个区域内对准剪切波信号的方法，比如，在共同待决美国临时专利申请序列号62/072,167中所描述的时间插值法，可用于校正非对准运动信号。在时间插值法中，来自跨不同脉冲回波事件的每个矢量的回波首先用于计算组织运动，包括由于剪切波和换能器压缩造成的变形所引起的运动。因此，在时间插值法技术中，组织运动在黑色实方形处测量。在每个矢量位置(被指示为图6的区域1中的白色圆形)处的时间插值可以对准每个区域内的组织运动信号。Methods for aligning shear wave signals within each region, such as the time interpolation method described in co-pending U.S. provisional patent application serial number 62/072,167, can be used to correct for non-aligned motion signals. In the time interpolation method, the echoes from each vector across different pulse-echo events are first used to calculate tissue motion, including motion caused by deformation due to shear waves and transducer compression. Therefore, in the time interpolation technique, tissue motion is measured at the black solid squares. Time interpolation at each vector position (indicated as the white circle in region 1 of Figure 6) can align the tissue motion signal within each region.
运动信号对准：将信号相移至公共时间网格Motion signal alignment: phase shifting signals to a common time grid
作为一个示例，通过将合适的相移应用于未对准的运动信号，运动信号可以被对准至公共时间网格。因为组织运动具有已知频率的正弦波，所以其允许附加方法来对准运动信号。假设由在区域1中的矢量V1检测的组织运动M1为，As an example, by applying appropriate phase shifts to the misaligned motion signals, the motion signals can be aligned to a common time grid. Since tissue motion has a sine wave of known frequency, it allows additional methods to align the motion signals. Assume thatthe tissue motion M1detected by vector V1 in region 1 is,
M1(t)＝D1·ejωt (5)；M1 (t) = D1 ·ejωt (5);
其中，D1是矢量V1的运动振幅，并且ω是超声换能器持续振动的频率。由在区域2中的矢量VN+1检测的组织运动将是，WhereD1 is the amplitude of motion of vectorV1 , and ω is the frequency at which the ultrasonic transducer continuously vibrates. The tissue motion detected by vectorVN+1 in region 2 will be,
其中，DN+1是矢量VN+1的运动振幅，并且(N·M)/PRF0是矢量V1与VN+1之间的时间延迟。exp(jω((N·M)/PRF0))的相移可以应用于等式(6)中的信号，使得时间与等式(5)中的对准。Where DN+1 is the amplitude of motion of vector VN+1 , and (N·M)/PRF0 is the time delay between vectors V1 and VN+1 . A phase shift of exp(jω((N·M)/PRF0 )) can be applied to the signal in equation (6) to align the time with that in equation (5).
这种相移方法可用于对准每个区域内的矢量，并且用于对准跨区域的矢量。This phase shifting method can be used to align vectors within each region, and to align vectors across regions.
在图7中示出了如上所述的区域对区域时间对准方法的示例。在此示例中，50Hz的持续振动曾用于在仿组织均匀体模内产生持续剪切波。用于剪切波检测的PRFe是500Hz，平行波束形成能力是4，成像矢量的总数是64，成像区域的数量是2，并且用于每个矢量的时间样本数量是24。在对准前，可以看到沿横向维度的剪切波信号的区域间不连续性。在通过时间插值法的区域内对准之后，校正了每个成像区域内的顺序跟踪延迟，如通过对剪切波信号斜率的仔细观察可以看出的。然而，区域间不连续性仍然存在，如等式(6)所预测的。在区域间时间对准之后，可以看出区域间不连续性被成功地去除(即，跨不同成像区域可以清楚地看到持续振动)。An example of the region-to-region time alignment method described above is shown in Figure 7. In this example, a continuous vibration of 50 Hz was used to generate continuous shear waves within a tissue-mimicking homogeneous phantom. The PRFe used for shear wave detection was 500 Hz, the parallel beamforming capability was 4, the total number of imaging vectors was 64, the number of imaging regions was 2, and the number of time samples used for each vector was 24. Before alignment, inter-region discontinuities in the shear wave signal along the lateral dimension can be seen. After intra-region alignment by time interpolation, the sequential tracking delay within each imaging region is corrected, as can be seen by careful observation of the slope of the shear wave signal. However, the inter-region discontinuities still exist, as predicted by equation (6). After inter-region time alignment, it can be seen that the inter-region discontinuities are successfully removed (i.e., the continuous vibration can be clearly seen across different imaging regions).
运动信号对准：参数拟合Motion signal alignment: parameter fitting
作为对准运动信号的另一个示例，跨多个时间点(帧)在给定像素处所检测的组织运动可以拟合至正弦时间函数，以便根据时间估计正弦波信号的振幅和相位。一旦已知正弦时间函数的振幅和相位，则可以计算在任何时间点的运动信号。因此可以估计每个像素的正弦信号的振幅和相位参数，并且然后可以计算在公共对准的时间网格处所有像素的运动信号。这种方法可用于利用每个区域内或跨区域的不同矢量所检测的时间对准像素。As another example of aligning a motion signal, tissue motion detected at a given pixel across multiple time points (frames) can be fit to a sinusoidal time function to estimate the amplitude and phase of the sinusoidal signal as a function of time. Once the amplitude and phase of the sinusoidal time function are known, the motion signal at any point in time can be calculated. The amplitude and phase parameters of the sinusoidal signal for each pixel can therefore be estimated, and then the motion signal for all pixels at a common aligned time grid can be calculated. This approach can be used to align pixels in time detected using different vectors within or across each region.
运动信号对准：使用正弦运动信号的2π移位的同步Motion signal alignment: synchronization using a 2π shift of a sinusoidal motion signal
作为又另一个示例，运动信号可以基于由换能器的持续正弦振动产生的组织运动的循环性质来进行对准。在这些实例中，在每个空间位置处的运动信号在时间上以周期T重复。周期T是由持续振动的角频率ω确定的，As yet another example, the motion signal can be aligned based on the cyclic nature of tissue motion produced by the continuous sinusoidal vibration of the transducer. In these examples, the motion signal at each spatial location repeats in time with a period T. The period T is determined by the angular frequency ω of the continuous vibration,
因此，正弦运动信号自身以相位差2π或时间周期T重复。因此，通过在图6中仔细设计时间延迟Δt可以时间上对准来自两个成像区域的运动信号，使得，Therefore, the sinusoidal motion signal repeats itself with a phase difference of 2π or a time period T. Therefore, by carefully designing the time delay Δt in FIG6 , the motion signals from the two imaging regions can be temporally aligned so that,
其中，k＝1,2,3,... (9)。 Where k = 1, 2, 3, ... (9).
因此，通过根据等式(9)选择时间延迟，来自不同成像区域的运动信号被“自动地”对准，而不需要进一步时间对准。Therefore, by selecting the time delay according to equation (9), the motion signals from different imaging areas are "automatically" aligned without the need for further time alignment.
基于等式(4和(9)，振动频率ω；检测PRF0；时间样本的数量M；以及每个区域内成像矢量的数量N都可以被微调以满足等式(9)中描述的条件。Based on equations (4 and (9), the vibration frequency ω; the detection PRF0 ; the number of time samples M; and the number of imaging vectors N in each region can all be fine-tuned to meet the conditions described in equation (9).
替代性地，“等待时间”ε以添加至检测区域之间，使得Alternatively, a "wait time" ε is added between detection regions, so that
因此，等待时间ε可以被方便地调节以满足等式(9)的要求，或每个区域的检测时间可以由外部触发信号启动，所述外部触发信号在正弦振动信号的不同周期上被同步至固定相位。需注意，区域内对准对于去除由区域内顺序跟踪引入的时间延迟而言仍然是有必要的。Therefore, the waiting time ε can be conveniently adjusted to meet the requirements of equation (9), or the detection time of each zone can be initiated by an external trigger signal that is synchronized to a fixed phase on different periods of the sinusoidal vibration signal. Note that intra-zone alignment is still necessary to remove the time delay introduced by sequential tracking within the zone.
运动信号对准：区域内处理Motion signal alignment: intra-region processing
如在图7中可以看到的，在区域内对准之后，每个成像区域内的组织运动信号被对准并且准备好用于机械特性计算。然而，在一些实例中，可以在每个单独的区域内计算组织机械特性，而不是跨不同成像区域对准运动信号，并且然后可以将来自不同区域的估计组合成一个最终图。以此方式，运动信号跨区域的不连续性将无关紧要。如果在区域之间最终机械特性图中存在较小的不连续性，则空间滤波器(例如，中值滤波器)可用于使最终机械特性图平滑。这种方法适用于持续换能器振动剪切波，因为主要剪切波传播方向是从上到下远离换能器。这种传播方向主要是在具有很少跨区传播的区域内，并且因此计算每个可行区域内的组织机械特性。As can be seen in Figure 7, after intra-region alignment, the tissue motion signals within each imaging region are aligned and ready for mechanical property calculations. However, in some instances, tissue mechanical properties can be calculated within each individual region, rather than aligning motion signals across different imaging regions, and the estimates from different regions can then be combined into one final map. In this way, discontinuities in the motion signals across regions will not matter. If there are small discontinuities in the final mechanical property map between regions, a spatial filter (e.g., a median filter) can be used to smooth the final mechanical property map. This approach is suitable for continuous transducer vibration shear waves because the primary shear wave propagation direction is from top to bottom away from the transducer. This propagation direction is primarily within regions with little cross-region propagation, and therefore tissue mechanical properties are calculated within each feasible region.
运动信号对准：单一成像区域检测Motion signal alignment: single imaging area detection
用于运动信号对准问题的另一种解决方案是避免使用多个成像区域(即，仅使用单一成像区域)。使用单一成像区域一般需要大量的成像矢量(即，N的较大值)以便覆盖足够大的成像区域。然而，这种方法的挑战是如果N很大，则PRFe将太低。低PRFe在造成混叠方面可以是难处理的，特别是对于由声学辐射力产生的瞬时和宽带剪切波。Another solution to the motion signal alignment problem is to avoid using multiple imaging regions (i.e., use only a single imaging region). Using a single imaging region generally requires a large number of imaging vectors (i.e., a large value of N) in order to cover a sufficiently large imaging region. However, a challenge with this approach is that if N is large, the PRFe will be too low. Low PRFe can be intractable in causing aliasing, especially for transient and broadband shear waves generated by acoustic radiation forces.
然而，对于由换能器振动产生的持续组织运动，可以通过利用用于驱动换能器的持续振动的正弦波的循环性质对混叠进行校正。如图8中所展示的，检测PRFe和振动频率ω可以被仔细地选择，使得通过移动脉冲回波事件(在图8中表示为圆形)整数倍正弦周期，可以重构非混叠运动信号。However, for sustained tissue motion produced by transducer vibration, aliasing can be corrected by exploiting the cyclic nature of the sine wave used to drive the sustained vibration of the transducer. As shown in FIG8 , the detection PRFe and the vibration frequency ω can be carefully selected so that by shifting the pulse-echo events (represented as circles in FIG8 ) by an integer multiple of the sine period, a non-aliased motion signal can be reconstructed.
在图8中示出的示例中，PRFe＝0.8ω/2π，这造成了混叠。通过将数据样本2、3、4和5分别移动一个周期、两个周期、三个周期以及四个周期，初始正弦信号可以被无混叠地重构。这可以针对单一成像区域内每个成像矢量来完成，以便获得非混叠剪切波信号。在此步骤之后，如上所述，跨不同矢量的附件时间对准然后可用于解释矢量之间的延迟。In the example shown in FIG8 , PRFe = 0.8ω/2π, which causes aliasing. The initial sinusoidal signal can be reconstructed without aliasing by shifting data samples 2, 3, 4, and 5 by one cycle, two cycles, three cycles, and four cycles, respectively. This can be done for each imaging vector within a single imaging region in order to obtain a non-aliased shear wave signal. After this step, the additional time alignment across the different vectors can then be used to account for the delays between the vectors, as described above.
在(例如，使用上述方法)对换能器运动的效应以及在超声脉冲回波运动检测中的时间延迟进行校正之后，在公共时间网格处的2D剪切波信号可用于使用标准弹性成像处理方法(比如，本振频率估计“LFE”、飞行时间、直接反演以及其他方法)来计算组织的机械特性。After correcting for the effects of transducer motion and time delays in ultrasonic pulse-echo motion detection (e.g., using the methods described above), the 2D shear wave signals at a common time grid can be used to calculate the mechanical properties of the tissue using standard elastic imaging processing methods (e.g., local frequency estimation "LFE", time of flight, direct inversion, and other methods).
在以上给出的示例中，假设超声换能器以单一频率进行振动。在此描述的方法还可以轻易地扩展至持续换能器振动包含多个正弦频率或啁啾信号的情况。如此，可以在多个频率上测量机械特性。In the examples given above, it is assumed that the ultrasonic transducer vibrates at a single frequency. The method described here can also be easily extended to the case where the continuous transducer vibration contains multiple sinusoidal frequencies or chirp signals. In this way, mechanical properties can be measured at multiple frequencies.
已经针对使用1D线性超声阵列换能器的2D弹性成像描述了以上技术。这些技术还可适用于单元素、1D弯曲阵列、1.5D阵列、1.75D阵列和2D阵列换能器。对于单元素换能器，所述方法可以向下缩放至1D弹性成像。对于2D阵列，所述方法可以扩展至3D弹性成像。还可以将对换能器运动的校正与超声运动检测中的延迟组合在一起。在此描述的方法还可用于测量组织和非组织材料(例如，聚合物)的机械特性。The above techniques have been described for 2D elastic imaging using a 1D linear ultrasonic array transducer. These techniques may also be applicable to single element, 1D curved array, 1.5D array, 1.75D array, and 2D array transducers. For single element transducers, the methods may be scaled down to 1D elastic imaging. For 2D arrays, the methods may be extended to 3D elastic imaging. Correction for transducer motion may also be combined with delays in ultrasonic motion detection. The methods described herein may also be used to measure mechanical properties of tissues and non-tissue materials (e.g., polymers).
已经根据一个或多个优选实施例对本发明进行了描述，并且应当理解的是，除明确陈述的以外，许多等价物、备选方案、变化和修改都是可能的并且在本发明的范围之内。The invention has been described in terms of one or more preferred embodiments, and it should be understood that many equivalents, alternatives, variations and modifications, except as expressly stated, are possible and within the scope of the invention.
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| CN202111304608.XACN113812979B (en) | 2015-10-08 | 2016-10-06 | System and method for ultrasound elastography using continuous transducer vibration |
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| CN201680058937.1ACN108135568B (en) | 2015-10-08 | 2016-10-06 | System and method for ultrasound elastography with continuous transducer vibration |
| PCT/US2016/055649WO2017062553A1 (en) | 2015-10-08 | 2016-10-06 | Systems and methods for ultrasound elastography with continuous transducer vibration |
| CN202111304608.XACN113812979B (en) | 2015-10-08 | 2016-10-06 | System and method for ultrasound elastography using continuous transducer vibration |
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| CN201680058937.1ADivisionCN108135568B (en) | 2015-10-08 | 2016-10-06 | System and method for ultrasound elastography with continuous transducer vibration |
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| CN202111304608.XAActiveCN113812979B (en) | 2015-10-08 | 2016-10-06 | System and method for ultrasound elastography using continuous transducer vibration |
| CN201680058937.1AActiveCN108135568B (en) | 2015-10-08 | 2016-10-06 | System and method for ultrasound elastography with continuous transducer vibration |
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| CN201680058937.1AActiveCN108135568B (en) | 2015-10-08 | 2016-10-06 | System and method for ultrasound elastography with continuous transducer vibration |
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